Tensile Stress-Induced Structural Changes Associated with Martensite Transformations in Fe-Mn-Si Based Shape Memory Alloys

摘要

Tensile specimens, with the chemical composition Fe-28Mn-6Si-5Cr (mass. %), were obtained by ingot metallurgy, hot rolling, solution treatment (1100℃/ 5 min/ water) and spark erosion cutting. Tensile tests were performed to failure and to prescribed strains, by loading-unloading. Ultimate strain and strength increased up to 80.8 % and 1033 MPa, respectively, with decreasing the cross section of specimens' gauge down to 2 mm2. The specimens were pre-strained by static tensile loading-unloading tests, to permanent strains as high as 60 %. This procedure aimed to stress-induce martensite, which was further analyzed, on the gauges of pre-strained specimens, by optical and scanning electron microscopy (SEM) as well as X-ray diffraction (XRD). Thermally induced reversion to austenite, of stress-induced martensite, was emphasized, during heating, by differential scanning calorimetry (DSC).